Also in the exercise fo the type "Show the charater for ..." it would be helpful, if you indicate alway the meaning in English under the Chines charcter!
Can "one second" be used the same way in Chinese as in English (e.g. someone asks you to do something and you say: one second!)
一秒 does not tend to have the figurative use that "one second" does in English.
I don't know if you can use 一秒 in Chinese like we do in English, but I know that I frequently hear 等一下 for the same effect, often said in quick succession.